The present invention relates to a data transferring device for communicating data between a plurality of nodes. More specifically, the present invention relates to a data transferring device capable of selectively using one of multiple data transfer rates between nodes.
As an international standard for high-speed serial bus transfer methods, the IEEE 1394-1995 standard has been known in the art. In this IEEE 1394-1995 standard, although it is possible to couple a plurality of nodes of different data transfer capabilities to a single bus, the maximum data transfer capability between two nodes depends on the maximum data transfer capability of a node existing between these two nodes. More specifically, three different data transfer rates of 100, 200, and 400 megabits per second (Mbps) are supported, and it is possible to learn the data transfer rate of a connection destination by the process of bus initialization or by the application of a speed signal just before a packet transfer.
Conventional data transferring devices in conformity to the IEEE 1394-1995 standard have some problems. For example, when a node having a high-speed data transfer capability (herein after called the high-speed node) is coupled to another having a low-speed data transfer capability (the low-speed node), it is not necessary for the high-speed node to use its internal circuit disposed for handling high-speed data transfers, therefore resulting in waste of bias to such a circuit.
The present invention was made with a view to providing a solution to the above-described problem with the prior art technology. Accordingly, an object of the present invention is to provide a data transferring device capable of configuring an optimal circuit according to the data transfer capability of a connection destination for achieving the reduction of power consumption.
In order to achieve the object described above, the present invention discloses a first data transferring device which is constructed of at least two nodes of which first and second nodes are coupled together by a bus, wherein the first node includes a detecting circuit for detecting the maximum data transfer capability of a connected node, at least two receiving circuits for receiving data from the bus, and a controlling circuit for selecting, based on an output signal from the detecting circuit, one of the receiving circuits and for performing control so as to bring the other of the receiving circuits to a stop, and wherein the second node includes a transmitting circuit for transmitting data to the bus and a notifying circuit for notifying the first node of its own maximum data transfer capability via the transmitting circuit.
The present invention discloses a second data transferring device which is constructed of at least two nodes of which first and second nodes are coupled together by a bus, wherein the first node includes a detecting circuit for detecting the maximum data transfer capability of a connected node, a receiving circuit for receiving data from the bus, a bias adjusting circuit for adjusting a bias for the receiving circuit, and a controlling circuit for controlling, based on an output signal from the detecting circuit, the bias adjusting circuit, and wherein the second node includes a transmitting circuit for transmitting data to the bus and a notifying circuit for notifying the first node of its own maximum data transfer capability via the transmitting circuit.